Process of making sheeting



J. B. WELLS arch 2, 1937.

PROCESS OF MAKING SHEETING Filed Feb. 15, 1932 Jackson/B Wells,

Patented Mar. 2, 1 937 UNITED STATES PATENT OFFICE PROCESS OF MAKING SHEETING Jersey Application February 15, 1932, Serial No. 593,147

1 Claim.

This invention relates to processes of making nitrocellulose films and similar products, especially processes in which the films are set by liquid baths instead of by evaporation. One object of the invention is to provide an inexpensive process of this nature which will produce flexible, transparent, nitrocellulose films, filaments, etc., rapidly with minimum fire-risk and with maximum recovery of the solvents employed. Another object is to provide a process of this nature which can be carried out in a relatively small and simple apparatus. A still further object is to provide a process in which cloudiness in the films is avoided in spite of the use of rapid or aqueous setting baths. Other objects will hereinafter appear. This application is in part a continuation of my application Serial No. 253,361, filed February 10, 1928, now Patent No. 845,377.

In the accompanying drawing the single figure is a diagrammatic side elevation, with the top broken away, of one form of apparatus in which my process may be carried out, the relative sizes of the parts being exaggerated for the sake of clearness.

I have found that the desired objects can be attained by shaping into film or filament form a nitrocellulose solution or dope containing methyl alcohol and a monohydroxy aliphatic alcohol of low volatility which is at least partially soluble in Water, and setting it, while in this form, by treatment with an aqueous bath. While plain cold water may be used, I prefer to employ a setting bath in which there is a nitrocellulose solvent, miscible with water but of insuflicient 35 amount to prevent the setting action, said solvent regulating the setting operation. For example, a bath of water and methyl alcohol has proven to be very useful.

The presence of an alcohol of low volatility in 40 the dope, such as normal butyl alcohol for instance, has been found to be of special benefit, during the setting step, because it lessens the danger of forming whitish or clouded defects in the film. In fact, typical rapid film-setting con- 45 ditions, which have produced clouded products from plain nitrocellulose-methyl alcohol dopes, have been found to produce clear transparent films when applied to similar dopes containing a higher alcohol. This tendency of the higher alcohols toward the formation of transparent films permits wider tolerances in the conditions of film-setting and allows higher speed of production without harm.

It is. a fortunate advantage of my film-forming operation that it fits in both with preceding and subsequent steps. For example, considerable dehydration of washed nitrocellulose fibers must be accomplished before a film dope can be made from them. The use of normal butyl alcohol for this purpose is disclosed in U. S. Patent No. 1,398,911, Seel, November 29, 1921. It forms a mass of nitrocellulose fibers containing about 40 to 60% of butyl alcohol. This, when dissolved in methyl alcohol, as described in U. S. Patent No. 1,380,258, Seel, Combs and Kemp, May 31, 1921, produces a dope having the desirable properties for making film by my present process. After the films are formed, they are coated to form photographic films; and the continued pres- 'ence of a higher alcohol, such as butyl alcohol, in such films promotes better wearing qualities and increased flexibility, as described in said lastnamed patent. It will, therefore, be seen that the higher alcohol passes successfully from the dehydration through my film-forming operation to the finished films, and is a beneficial ingredientnot a passive diluent-during such operation.

I shall now describe one way of carrying out my process, by way of illustration, but it will be understood that the invention is not limited to the details thus given, except as indicated in the appended claim. 100 parts by weight of cellulose nitrate fibers, of the type usually made up into film, are dehydrated with butyl alcohol and pressed until they contain from 30 to 100, say 50, parts by weight of butyl alcohol in the mass, as indicated in the hereinabove cited patents. This mass is then dissolved in 300 to 1000 parts by weight, say 500 parts, of methyl alcohol and the ingredients thoroughly stirred, say in a mixing apparatus, until the solution is substantially'homogeneous.

This viscous dope, after filtering, if necessary, is then loaded into the V-shaped trough I of the apparatus shown in the drawing. The lower part of this trough is provided with accurate edge pieces 2, 3, the latter being regulated up and down by the screw 4, thereby regulating the thickness of the film from dope 6. Edge piece 2 projects slightly below edge piece 3, thus guiding the accurately gauged film-shaped dope onto the accurately polished cylindrical surface 1 .of wheel 8. This surface may be that shown in U. S. Patent No. 1,466,733, Sulzer, September 4, 1923, but any other suitable surface, such as polished electro-deposited chromium, may also be used. The wheel 8 turns in the direction of the arrow, the sheet of .dope on the surface 1 passing through a chamber 9. In this chamher the film-shaped body 5 of dope is still in a slowly flowable condition and can, therefore, settle under the influence of gravity sufficiently to enable the thickness of the layer to equalize. In other words, if portions of the layer are slightly too thick and other portions are slightly too thin, in spite of the accuracy of edge pieces 2 and 3, these inequalities will gradually work out in chamber 9 by the settling of the higher portions and the raising of the lower portions.

The equalized film-form layer 5 is then carried by continued revolution of the wheel 8 into the setting bath IE]. The latter can be conveniently contained in a vessel which is substantially concentric-with and spaced from the outer surface 1 of the wheel 8, as indicated in dotted lines in the drawing. While other formsmay be used, this has the advantage of enabling the liquids of the bath to enter by pipe H and pass in a direction counter to the movement of the film, finally leaving the apparatus through exit pipe l2. As the setting bath proceeds from pipe II to pipe l2 in the direction of the arrows, it becomes more and more charged with methyl alcohol, which it extracts from the layer 5 on the surface 1. Conversely the layer 5 starts to set when it enters the bath adjacent the pipe l2 and gradually gives up more and more of its methyl alcohol to the bath as it proceeds toward the entrance pipe H. In other words, the more firmly the film becomes set and the more it loses the methyl alcohol, the stronger is the setting bath with which it contacts. Since the bath, when it leaves pipe [2, contains its maximum percentage of methyl alcohol, it is in the best condition for the recovery of the latter by the usual processes, say by fractional distillation.

While I can introduce plain Water through pipe H as the initial ingredient of the setting bath, and allow the latter to increase in methyl alcohol content, as it extracts methy1 alcohol, during its passage through the apparatus, I prefer to introduce through the pipe 9 l a mixture of a non-solvent for the nitrocellulose, such as water, and a solvent for it, such as methyl alcohol. A 50% aqueous solution by weight of methyl alcohol has proven to be very useful. This becomes stronger as it proceeds through the apparatus to the exit pipe l2, by reason of the extraction of methyl alcoho1 from layer 5 and entrance of water into the film.

Of course, in any event there is some extraction of the higher alcohol, such as butyl alcohol, from the film, but there is always a substantial amount of it left in the film to maintain flexibility and wearing qualities in the latter. In fact, the rotation of the wheel 8, the rate of flow of the bath it, the strength of the bath Ill, and the length of the bathing chamber are always coordinated so as to leave the film with a useful content of the higher alcohol,-say of the order of l to 10% of the weight of nitrocellulose; but this may be considerably higher, say 20%, depending upon the extent of curing or drying after the set film is stripped from the surface 1. It will thus be seen that there is considerable latitude in the content of butyl alcohol in a film which is strong enough to be stripped, but a useful residuum of this alcohol always remains. In fact, even a considerable amount of methyl alcohol may remain in the stripped film and be removed by subsequent drying or curing operations, such as heretofore used on films formed by evaporation. Any higher alcohol which is taken up by the bath Hi can readily be recovered by fractional distillation and used again. Its presence in the bath does not interfere with the action of the latter.

Between the point where the set film 5| is stripped from the surface I and the point where the layer 5 of dope is deposited upon I, there may be located any suitable cleaning or polishing apparatus, such, for instance, as that described in U. S. Patent No. 1,187,929, Reid, June 20th, 1916. A pipe i5 is provided with fine perforations in its under side through which water is sprayed onto the surface I. This pipe is parallel to theaxis of drum 8. The cleaning liquid is not allowed to flow down the surface I to the stripped film 5| or the bath 10, but is taken up by a dam in the shape of a hollow roll l6 having its periphery covered with a layer of soft rubber I"! through which a series of fine apertures are provided communicating with the interior of the roll, the latter being connected to a vacuum apparatus, thus sucking the water through the dam and out of the apparatus. The surface of the drum may be given a final conditioning by an absorbent roll l9, held against the surface by an adjustable spring 20.

Since the inner side of the film, which is stripped from the surface I, is kept from contact with liquids, and since the outer surface passes over smooth roll [3, and is squeegeed by the latter, the film 5E carries little or no surface liquid, and is in condition to be dried, cured and coiled by the known methods heretofore used in the production of nitrocellulose films by evaporation.

The trough I may be kept above room temperature, if desired, to keep the dope 6 at the right viscosity for formation of the layer 5, and may be covered to prevent the loss of volatile solvents. Both of these expedients, being well known in the art are, for the sake of simplicity, omitted from the drawing. The bath Iii may vary in temperature over a considerable range, although, in general, it is preferable to operate at lower temperatures, the higher the percentage of water in the bath iii. For example, if pure water be introduced through pipe II, a temperature of about 4 C. is useful. 50% or more of methyl alcohol, there is no need for such low temperature. I usually prefer, however, to keep the entire apparatus, with the exception of trough i, at or below room temperature, say 23 0., because with higher temperatures the tendency towards cloudiness becomes greater.

My process may be applied to films of thicknesses customarily employed in the photographic art, but thicker ones, and even somewhat thinner ones, may be obtained in a state of satisfactory transparency, fiexibility and strength. The setting action imparts sufficient strength to the film to allow it to be stripped from the surface l; in fact, the setting action seems to counteract any harmful sticking tendency of the dope on the surface I.

While I prefer to use normal butyl alcohol, because it is most readily available commercially, my process may be carried out with other monohydroxy aliphatic alcohols having a low volatility, such as isobutyl alcohol, and the different isomeric amyl alcohols, or mixtures of them, commonly available in fusel oil. It will be noted that these all have boiling points somewhat above that of water.

In the preferred form of my process the methyl alcohol used in the dope. contains less than 1% But with baths containing of water and the dehydrated nitrocellulose fibers containing the butyl alcohol contain less than about 2 or 3% of water. Consequently, the water content of the mixed dope is of the order of 1%. There is no objection to carrying the dehydration below this point, but the solvent power of methyl alcohol for nitrocellulose rapidly falls off as the water content increases, so it is undesirable to exceed the percentages given.

While I have indicated a cylindrical Wheel surface as a suitable one to carry the film-shaped dope when it passes through the setting bath, it will be understood that any of the well known forms of surfaces may be substituted, such as a belt having a polished even face.

From the foregoing, it will be observed that my process is additionally characterized by regulation or adjustment of the ability of the precipitating or hardening bath to precipitate the material of the web or film. This comprises regulation of the concentration of the cellulose ester solvent in the precipitating fluid, regulation of the temperature of the bath and regulation of the speed of passage of the bath with respect to the web or film during precipitation thereof.

It is advantageous that the concentration of the solvent, methyl alcohol, for example, in the fiuid entering the precipitating chamber be maintained at such a value that the fluid as a Whole will have the desired effect on the web or film as it progresses through the bath. As indicated elsewhere in the specification, a preferred concentration of methyl alcohol is in the neighborhood of 50%. In order to maintain the bath at this preferred concentration I keep a careful check on, and control of, the solvent content of the bath as it enters the precipitating chamber. As it progresses through the precipitating chamber it picks up more and more solvent from the film. As above indicated, a bath having a low concentration of alcohol therein will more readily precipitate the film, and a higher speed of manufacture could thus be employed, but it may be desired to operate at a temperature higher than that which would be suitable for that bath and one needs merely to increase the alcohol content of the bath to a point suitable for that temperature. Of course, there is a limit to the alcohol concentration of the bath as too high a concentration would undesirably reduce speed of manufacture and might even not completely set the film.

Control of the temperature of the bath is thus an important element entering into the regulation of the ability of the bath to accomplish its precipitating action on the plastic material. The temperature should be low enough to prevent the concentration of the solvent from falling below the desired figure by evaporation losses and must be kept sufiiciently low for that particular alcohol concentration to avoid cloudiness in the film. The temperature used, also depends upon the amount of solvent present in the bath as originally introduced, since a bath containing a less amount of solvent requires the maintaining of a lower temperature than is the case with a bath containing a greater amount of solvent. The rate of flow of the bath with respect to the film may also be regulated in order to obtain an emcient precipitating action, i. e., the length of time which the film is permitted to remain in the particular bath should, of course, be long enough to cause sufficient precipitation of the film for it to be safely stripped from the film-forming surface.

Thus, it becomes apparent that I may adjust the ability of the precipitating bath to coagulate the film by regulating any one or more of three factors-temperature, concentration and relative speed of bath. These three are coordinated in such a way as to give maximum efiiciency of operation and quality of product. If one or two of the factors are held constant the third factor is adjusted to give best results or two or three of the factors may be simultaneously adjusted to give the desired results.

It will thus be apparent that regulation of the ability of the bath of fluid to precipitate the material of the web can be accomplished by a coordination of several or all of the various factors of control of concentration of solvent and control of temperature and of speed of fiow of the fluid with respect to the web.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

The method of forming a continuous, clear, transparent sheet from a mass of plastic material containing a solvent therefor which consists'in passing the plastic mass in web-like form into a bath of aqueous alcoholic precipitating liquid containing a solvent and a non-solvent for the plastic material and adjusting the ability of the liquid to precipitate the plastic material by continuously coordinating and regulating the concentration of solvent in the liquid with respect to the temperature of the liquid and with respect to the speed of movement of the bath in relation to the movement of the web, the ratio of solvent to non-solvent in the bath, the temperature and speed being so selected as to produce an initially clear sheet and to continuously maintain the sheet in clear, transparent condition during precipitation.

JACKSON B. WELLS.

CERTIFICATE OF CORRECTIQN.

Patent No. 2,072,145. March 2, 1957.

JACKSON B. WELLS.

It is hereby certified that error appears in the printed specification e! the above numbered patent requiring; correction as follows: Page 1, first column, line 18, for the patent number "845,577" read 1,845,577; and that the said Letters Patent should be read with this correction therein that the same may conform to the record. of the case in the Patent Office.

Signed and sealed this 27th day of April A. D. 1937.

Leslie Frazer (Seal) Acting Commissioner of Patents. 

